The present invention relates generally to lighting, and more particularly to reflector lamps including an optical interference filter to tailor the transmitted light energy.
Thin film optical interference coatings, known as interference filters or optical interference films, which comprise alternating layers of two or more materials of different refractive index are well known to those skilled in the art. Such coatings or films are used to selectively reflect and/or transmit light radiation from various portions of the electromagnetic spectrum such as ultraviolet, visible and infrared radiation. These films or coatings are used in the lamp industry to coat reflectors and lamp envelopes.
One application in which these coatings have been found to be useful is applied to reflectors in the form of what is known in the art as cold mirrors. A cold mirror is a glass or plastic reflector coated on the inside reflecting surface with an optical filter which reflects visible light, thereby projecting it forward of the reflector, while at the same time permitting longer wavelength infrared energy to pass through the coating and the reflector. This insures that the light projected forward by the reflector is cooler than it would otherwise be if both the visible and the infrared light were reflected and projected forward.
Multi-layer optical inference filters and their use with reflector electric lamps is well known to those skilled in the art. Commercially available, high efficiency lamps including an optical interference filter have achieved considerable commercial success such as the Halogen-IR available from General Electric Company. This lamp includes a double ended light source (such as a halogen-incandescent lamp) mounted inside a parabolic reflector.
Optical interference filters are often made of alternating layers of refractory metal oxides having high and low indexes of refraction. Refractory metal oxides are used because they are able to withstand the relatively high temperatures (e.g 400xc2x0 C. to 900xc2x0 C.) that develop during lamp operation. Such oxides include, for example, titania, hafnia, tantala and niobia for the high index of refraction material and silica or magnesium fluoride for the low index of refraction materials. Examples of these types of filters are provided in U.S. Pat. Nos. 5,143,445 and 5,569,970, herein incorporated by reference, wherein these materials provide high reflectance in the visible spectrum between, for example, 380 to 770 nanometers.
Typically, cold mirror coatings are based on combining two or more reflectance arrays. A high reflectance array consists of alternating layers of high and low index films, each layer having an optical thickness of one Quarter-Wave Optical Thickness (QWOT). The optical thickness is defined as the product of the physical thickness times the refractive index of the film. The QWOT is referenced to a conveniently chosen design wavelength. For example, at a design wavelength of 500 nm, a QWOT equals 125 nm. Since a single high reflectance array reflects across only a portion of the visible region, two or more arrays must be combined for an extended high reflectance band across the visible spectrum.
Cold mirror reflectors have achieved a high degree of acceptance in display lighting applications where their high degree of reflectance of visible light of the proper color temperature has been found very attractive. Therefore, a combination of high visible reflectance, good color maintenance over the life of the reflector, and the ability to select varying degrees of infrared and ultraviolet reduction have emerged as important factors in lighting coatings.
The subject invention is provided to minimize the temperature in the vicinity of the lamp, helping to reduce oxidation and other physical degradation thereof.
According to an exemplary process for manufacture of the invention, a reflector for a lamp comprised of a body having a generally parabolic shape is coated on its interior and exterior surfaces with a light reflective coating. Preferably, chemical vapor deposition is utilized for the coating process. Thereafter, the coating on the external surface adjacent a cavity in the closed end of the reflector body is removed.
Exemplary embodiments of the invention can be used to improve the performance in various types of reflector lamps including arc discharge lamps, incandescent lamps and halogen lamps. In this regard, the invention is also directed to the reflector formed via the inventive process. Moreover, the reflector is generally a parabolic shaped body including one generally closed end and an opposed open end. The closed end includes a cavity housing the base of the lamp. Electrical connections are provided through the closed end of the reflector and the lamp cemented therein. A light reflecting coating is included on both the internal and external surfaces of the reflector body. However, the external surface of the reflector body adjacent the cavity is substantially devoid of the coating.